The present invention relates to a hard coat film. More specifically, the present invention relates to a hard coat film having an inorganic hard coat layer having excellent scratch resistance and weatherability, in which curling is inhibited from being generated and which is particularly suited for sticking on outside faces of window glasses and plastic boards for windows in lofty buildings and affixing on show windows.
Plastic films having various functions, for example, at least one of a ultraviolet (hereinafter referred to as xe2x80x9cUVxe2x80x9d) ray-shielding function, an infrared ray-shielding function, a see-through preventing function, contamination preventing function and a broken piece-scattering preventing function have so far been used as films for sticking on window glasses and plastic boards for windows (hereinafter called a window film) for various purposes.
In recent years, it has been found that semiconductors such as titanium oxide have a strong photocatalytic action, and since then, development of photocatalysts and researches thereof for putting them to practical use have actively been carried out. In these photocatalysts, when a semiconductor represented by, for example, titanium oxide is excited by light having energy higher than in a band gap thereof, an electron is produced in a conduction band, and a positive hole is produced in a valence band, wherein this electronxe2x80x94positive hole pair which is rich in energy is utilized. Investigated by applying such photocatalytic action are, for example, decomposition and removal of various substances which are contained in waste water and waste gas and which are problems on environmental pollution, deodorization, prevention of contamination, antibacterial treatment and sterilization.
Further, it is known that in such photocatalysts, irradiation thereof with light having energy higher than in a band gap produces, as described above, an electron in a conduction band of the photocatalysts and a positive hole in a valence band thereof and that this action of an electron and/or a positive hole provides the surface with polarity to provide it with extrahydrophilicity.
Accordingly, it has been tried to provide a photocatalytic function layer on the surface of window film making use of such extrahydrophilicity and contamination prevention performance of a photocatalyst and stick this film on the outside surface of window glass. This trial aims to naturally clean (self-cleaning) stains (organic matters) stuck on the film surface by repetition of irradiation with sunlight and rain-fall without cleaning them by making use of the extrahydrophilicity and contamination prevention performance thereof and to prevent the window glass from being clouded and secure visibility in rainy weather.
In such window film, a hard coat layer is usually disposed for the purpose of providing it with a scratch resistance. This hard coat layer is classified roughly into an organic base and an inorganic base, and known as the organic base hard coat layer is a layer obtained by applying on a base film, for example, an ionizing radiation-curing type resin composition such as a polyester acrylate base, an epoxy acrylate base, a urethane acrylate base and a polyol acrylate base and curing it. On the other hand, known as the inorganic base hard coat layer is a metal oxide layer formed by a sol-gel method, for example, a cured matter layer of a silane compound. In such hard coat layers, the inorganic base hard coat layer is advantageous when, for example, a photocatalytic function layer is disposed thereon, since if it is the organic base hard coat layer, the above hard coat layer is quickly deteriorated by virtue of a photocatalytic function. However, though the inorganic base hard coat layer is excellent in a scratch resistance, contraction takes place in the layer comprising metal oxide in curing when the layer comprising metal oxide is formed by the sol-gel method, and curling can not be avoided from being generated in the film. In addition thereto, there is the problem that it does not have a satisfactory weatherability and is liable to cause cracks with the passage of time.
The present invention has been made under such circumstances, and an object thereof is to provide a hard coat film having an inorganic hard coat layer having excellent scratch resistance and weatherability and, if desired, provided thereon a coating layer having various functions, in which curling is inhibited from being generated and which is suited particularly for sticking on outside faces of window glasses and plastic boards for windows in lofty buildings and sticking on show windows.
Intensive researches repeated by the present inventors in order to achieve the object described above have resulted in finding that capable of being suited to the object is a film or a laminate which has a specific structure and in which a hard coat layer comprises a cured layer of a mixture containing metal oxide particles and a silane compound. The present invention has been completed based on such knowledge.
Provided are:
(1) A hard coat film which comprises a laminate wherein a primer layer and a hard coat layer comprising metal oxide particles and a cured matter of a silane compound are laminated in order on one face of a base material,
(2) the hard coat film as described in the above item (1), wherein a coating layer is further provided on the hard coat layer,
(3) the hard coat film as described in the above item (2), wherein the coating layer is a layer having at least one function selected from a photocatalytic function, an infrared ray-shielding function, a UV ray-shielding function, an antibacterial function, a contamination preventing function, an antistatic function, a color developing function and a cloudiness preventing function,
(4) the hard coat film as described in the above item (3), wherein the coating layer is a photocatalytic function layer, and the base material comprises polycarbonate, and
(5) the hard coat film as described in any of the above items (1) to (4), wherein an adhesive layer is provided on the other face of the base material.
FIG. 1 is a cross section showing one example of the structure of the hard coat film of the present invention.